There has been need in ophthalmology for a nonirritating and chemically inert colloid which would dissolve in water to produce a viscous, colorless solution having a high degree of transparency and a refractive index similar to that of the cornea. Such a solution would be useful as a bland vehicle for ophthalmic medicaments, as a substitute for natural secretions in cases of keratoconjunctivitis sicca and as an emollient and cohesive solution to be used with contact lenses and gonioscopic prisms. Attempts have been made to adapt various compounds for these purposes, with only partial success. Acacia, tragacanth and gelatin have been most widely used, but they are chemically unstable, have high refractive indexes and are good mediums for the growth of bacteria and fungi. A synthetic substance, methyl cellulose,1 has considerable advantages over these naturally occurring gums. Its properties and some of its ophthalmic uses are reported here. Methyl cellulose